The invention relates to an additive composition and concentrate for two-cycle oils. The additive, when incorporated into two-cycle oils, produces a dispersant additive composition which will provide satisfactory engine cleanliness and importantly will render the oil stable after being subjected to low temperatures. The additive compositions of the invention substantially delays or avoids the formation of gelled agglomerates which in previous prior art products have become a concern with respect to engine performance.
Two-cycle (two-stroke) internal combustion engines, including rotary engines are found in power lawn mowers and other power-operated gardening equipment, power chain saws, pumps, electrical generators, marine outboard engines, snowmobiles, motorcycles, and the like. Two-cycle engines employed as such are operated by mixing the fuel and the two-cycle oil in prescribed proportions. The two-cycle oil additive of the instant invention is designed for use in most types of two-cycle engines and particularly in water-cooled marine outboard engines.
Two-cycle engines are lubricated by mixing the lubricant with the fuel for the engine. The mixture of fuel and lubricant passes through the crankcase of a two-cycle engine, where it lubricates the moving parts of the engine, and then flows through intake ports into the combustion chamber of the engine where the mixture of the fuel and lubricant is burned. The combustion products are vented from the combustion chambers through exhausts ports. As a consequence, a satisfactory lubricant for a two-cycle engine must not only provide adequate lubrication for moving engines parts but also must be able to pass into the combustion chamber leaving no objectional deposits in the intake ports; must burn cleanly to avoid fouling the combustion chamber and spark plug with undesirable deposits; control varnish and sludge formation which leads to ring sticking and in turn to failure of the sealing function of piston rings; and must not result in plugging of the exhaust ports.
The increasing severity of the conditions under which two-cycle engines operate, has led to increasing demands for oils to adequately lubricate such engines. Alleviation of the problems has been through the provision of more effective additives for two-cycle engine oils and oil fuel combinations.
It is known to use acylated nitrogen-containing compounds as dispersant in two-cycle oil lubricants to prevent the deposition of solid materials on engine surfaces in contact with the lubricating composition. Such acylated nitrogen-containing compounds, as for instance the reaction product of isostearic acid and a polyamine, are disclosed in U.S. Pat. Nos. 3,110,673 and 4,705,643. These products are, however, susceptible to forming gel like agglomerates called "fish-eyes", when subjected to low temperatures as experienced in storage. The matrix for the gels are thought to be compounds formed during synthesis. The gel can be observed by inverting a glass vial of dispersant in oil and watching for the globules or agglomerates which adhere to the glass surface. Once formed, the gel is stable at room temperature and can cause blocking of the filters of the two-cycle engines in addition to rendering the oil lumpy and aesthetically displeasing for marketing purposes.
U.S. Pat. No. 3,110,673 mentioned above discloses a lubricant composition containing a pour point depressant and ashless dispersant. The ashless dispersant is described as the reaction product of a polyalkylene amine and a mixed, branched and straight chain acid.
U.S. Pat. No. 4,705,643, also mentioned above, described an ashless lubricating two-cycle oil-additive comprised of the condensation reaction product of a branched isostearic acid and tetraethylene pentamine.
U.S. Pat. No. 2,568,876 discloses the use of organic nitrogen compounds as corrosion inhibiting compositions. The organic nitrogen compound disclosed are reaction products of monocarboxylic acids, and polyalkylene polyamines having one more nitrogen atom per molecule than there are alkylene groups in the molecule, which are further reacted with an alkenyl succinic acid anhydride. The ratio of alkenyl succinic acid to monocarboxylic acid disclosed is 1:1 to 4:1 and the alkenyl radical carbon range disclosed preferably range from 8 to 18.
U.S. Pat. No. 3,216,936 discloses nitrogen-containing compositions derived from the acylation of alkylene amines and is used to stabilize metal phosphorodithioates antioxidant additives in lubricating compositions. The acylated amines of the patent are prepared by heating together an alkylene amine with an acidic mixture consisting of a hydrocarbon-substituted succinic acid and an aliphatic monocarboxylic acid. The equivalent amount of succinic acid to monocarboxylic acid disclosed range from 1:0.1 to about 1:1.
U.S. Pat. Nos. 4,200,545; 4,708,809; 4,663,063; 4,708,809 and 4,780,111 all disclosed products derived from reacting first and second acylating agents comprising carboxylic acids or anhydrides with polyamines wherein the range of equivalence for the succinic acid agent to monocarboxylic acid ranges from 1:1 to 10:1.
Copending U.S. application U.S. Ser. No. 742,955, filed Aug. 9, 1991, incorporated herein by reference and U.S. Ser. No. 869,282, and U.S. Ser. No. 869,281 filed contemporaneously with the instant application all disclose compositions for two-cycle oils and especially two-cycle water-cooled outboard engines. U.S. copending application Ser. No. 742,955 discloses controlling gel formation in two-cycle oil with an additive comprising a reaction product of a monocarboxylic acid, a polyalkylene polyamine and a high molecular weight acylating agent. The application further disclosed additive compositions also containing a polyolefin and a pour point depressant flow improver.
The present invention is directed to an additive for two-cycle lubricating oils especially two-cycle oil additives for water-cooled outboard engines. The invention is further directed to an additive which is stable at low temperatures and which additionally provides good detergency, lubricity, antiwear and corrosion inhibition.
It is therefore an object of the invention to provide a low temperature stable two-cycle oil additive which will not form gels at low temperatures and which provide satisfactory engine cleanliness.